1. Field of the Invention
The present invention relates to a lens driving mechanism of an image pickup apparatus, and an image pickup apparatus using the lens driving mechanism
2. Description of the Related Art
In recent image pickup apparatuses such as cameras, auto-focus mechanisms capable of freely changing a focal length at the time of picking up images within a given range are employed. There is an increasing demand for the image pickup apparatuses to have a higher magnification and larger aperture. Generally, in the auto-focus mechanisms, at least either mechanical compensation in which movement of a focal plane is compensated for by nonlinear movement of a lens group using a cam, or optical compensation in which a focal plane is designed to remain constant even after zooming is effected by calculating an optical power balance is employed and is used in combination with electronic compensation in which movement of a focal plane is compensated for by using an auto-focus function of the image pickup apparatus. This is because the focal plane movement of a zoom lens having a high magnification and large aperture is difficult to compensate for to a sufficient level by using only the mechanical compensation or the optical compensation.
As shown in FIGS. 13 and 14, in a lens driving mechanism of a conventional image pickup apparatus, a driving force is transmitted from the end of a rotating shaft of a DC motor 61 to a first drive gear 62 via belt drive, and a rotor 70 connected to a motor power transmission ring 67 is rotated via multiple clutch gears 63. Accordingly, a lens driving ring 68 mounted on the inside of the motor power transmission ring 67 is rotationally driven.
For example, a lens frame driving apparatus disclosed in Japanese Patent Laid-Open No. 2006-71942 as a lens driving mechanism includes: at least one vibrator for generating elliptical vibration composed of bending standing-wave vibration and longitudinal vibration; an electrically-driven member linearly driven in an optical axis direction relative to the vibrator by the action of the elliptical vibration of the vibrator; a manually-driven member provided movably in the optical axis direction in accordance with manual operation; and a driven member in which a rolling element in pressure contact with the outer surface of the electrically-driven member and the inner surface of the manually-driven member to be rollable in the optical axis direction is disposed, and which is linearly moved in the optical axis direction along with the rolling element that rotates to move in response to the relative movement of the electrically-driven member and the manually-driven member in the optical axis direction.
In a vibration wave motor and a lens barrel disclosed in Japanese Patent Laid-Open No. 2006-158054, a lens in a lens barrel is drive-controlled by a vibration wave motor for bringing at least one vibrator including a driving element excited to perform elliptical vibration, and a node of vibration into frictional contact with a contact surface provided perpendicular to a rotation axis direction in a rotor supported to rotate about the rotation axis, and rotationally driving the rotor, the vibration wave motor including a support member, a guide support portion formed in the support member, the guide support portion supporting the vibrator substantially at the node of vibration while restricting movement of the vibrator in a direction perpendicular to the rotation axis and a circumferential direction and enabling linear movement of the vibrator along the rotation axis direction, and an urging member arranged in the support member, the urging member urging the vibrator in the rotation axis direction of the rotor so as to be in contact with the contact surface, wherein the vibrator, the rotor, the support member, and the urging member are integrated into a unit to form the vibration wave motor.
However, conventionally, in the lens driving mechanism as shown in FIGS. 13 and 14, multiple gears need to be arranged between the rotating shaft of the DC motor 61 and the motor power transmission ring 67. Thus, there is a limit in ensuring the driving accuracy and downsizing as the lens driving mechanism, and it is difficult to further reduce the size of the lens driving mechanism. The lens driving mechanism also has a disadvantage that it lacks tranquility with the driving sound of the gears at the time of rotation being loud since each gear of the multiple gears is set with a given reduction ratio.
A lens frame apparatus in which the lens frame driving apparatus disclosed in Japanese Patent Laid-Open No. 2006-71942 is incorporated includes an ultrasonic actuator mounted on a fixed frame via a mounting plate. A movable frame with which the vibrator of the ultrasonic actuator is in pressure contact is fitted to the outer peripheral portion of the fixed frame in a forward/backward movable manner. A driven frame is fitted to the outer peripheral portion of the movable frame, and an outer frame is fitted to the outer peripheral portion of the driven frame respectively in a forward/backward movable manner. A roller is incorporated in the driven frame in a state of pressure contact with the movable frame and the outer frame. When the movable frame is electrically driven by the actuator, the driven frame is forwardly/backwardly driven via the roller in accordance with the forward/backward movement of the movable frame. On the other hand, when the outer frame is forwardly/backwardly driven by manual operation, the driven frame is forwardly/backwardly driven via the roller in accordance with the forward/backward movement of the outer frame. The technique disclosed in Japanese Patent Laid-Open No. 2006-71942, however, has a problem that it is not possible to increase the aperture size of a lens incorporated within a lens frame, and reduce the size of the lens frame at the same time since the ultrasonic actuator is mounted inside the lens frame.
The vibration wave motor disclosed in Japanese Patent Laid-Open No. 2006-158054 includes a housing, a rotor, a bearing member, a vibrator serving as an actuator and having a support shaft and a driving element, and a leaf spring having a pressing protrusion. The vibrator is slidably disposed in an opening of the housing along the rotation axis direction with the support shaft being supported in a rotatable manner. The vibrator is held while being urged by the leaf spring and being in contact with the rotor. The vibrator is excited to generate supersonic vibration so that the rotor is rotated. Since the vibrator is movably supported by the housing in the rotation axis direction and the vibrator is urged by the leaf spring and is in contact with a friction contact surface of the rotor, the vibrator is evenly in contact with the rotor in a direction perpendicular to the friction contact surface so as to provide superior driving conditions of the vibration wave motor. That is, in the lens barrel of Japanese Patent Laid-Open No. 2006-158054, the vibrator is rotated in contact with the rotor as a plane perpendicular to an optical axis in the lens barrel, to thereby drive the lens barrel by use of the torque. The technique, however, has a problem that the driving accuracy is relatively low as compared with a case of directly driving the lens barrel since the lens barrel is driven via a predetermined power transmission mechanism.
Accordingly, there has been a demand for a lens driving mechanism for an image pickup apparatus capable of being reduced in size, and having excellent driving accuracy and tranquility.